The invention relates to the beneficiation of minerals in fine ore pulps by froth flotation.
Froth flotation is a widely practiced process for separating multicomponent minerals and ores into their components. The process is amenable to a large variety of minerals and ores and provides in many instances, a highly economical and efficacious method for concentrating components of minerals and ores.
There are, however, several limitations to froth flotation processes. One of the most serious drawbacks to these processes is that very finely sized feed, such as feed comprising particles passable through a 200 mesh screen, and particularly those of -10 microns or finer, are not effectively concentrated by froth flotation. Such very fine particles or slimes may be naturally occurring constituents of a mineral or ore or may be artificially produced during the grinding of the mineral or ore to a suitable size for mineral liberation. It is well-known to those skilled in the art that certain materials will not float in a froth flotation process when ground to an exceedingly fine size, although they will float under the same conditions when provided in coarser grain size.
At any rate, those who have heretofore attempted to concentrate components of various finely sized minerals and ores by froth flotation have met with little success. Accordingly, they have advocated desliming prior to flotation, when possible, although such practice adds to the processing costs and loss of valuable mineral. Further, it is general practice to desist, when possible, from grinding certain ores and minerals to a degree at which finely sized minerals or slimes are artificially produced.
In many instances, finely sized minerals or slimes cannot be avoided and removed, when present, for economic or practical reasons. For example, kaolin clay is a naturally slimed mineral, consisting predominantly of particles 2 microns or finer. This clay is mechanically associated with very finely divided color body impurities which detract from the value and utility of the clay in many applications. Prior art efforts to beneficiate the clay by floating the color body impurities have met with mediocre success at best unless the clay feed was prefractionated to reduce the quantity of fines. Certain relatively coarse grained minerals and ores, too, have defied effective froth flotation since they are not readily reduced to suitable flotation feed size without provision of fines when they are ground to overcome interlocking between dissimilar mineral genera to permit their flotation. As examples of ores which become slimed when ground for flotation feed may be cited cassiterite ores, taconite ores, magnesite-brucite ores and uraninite ores (from which concentration of uranium values are desired). Other examples are well-known to those skilled in the art. The technical literature is replete with reports of poor results in beneficiating such slimed minerals and ores by froth flotation without prefractionation or desliming.
One method of beneficiation by froth flotation of the minerals in fine ore pulps is by the use of carrier particles. Greene et al., U.S. Pat. No. 2,990,958, teach a process for the froth flotation of very finely divided multicomponent mineral masses in which the finely divided or slimed feed is conditioned with (1) a reagent capable of selectively oiling a desired component of the feed for entry into the froth during the concentration step, and (2) a particulate auxiliary mineral which is collector-coated (oiled) in a manner such that it is also capable of entry into the froth during the concentration step, thereby enhancing or promoting the flotation of the selectively oiled fraction of the feed. The feed, thus conditioned and in the form of an aqueous pulp is subjected to froth flotation, thereby producing (1) a froth product which is a concentrate of the oiled water-repellent component of the feed in intimate association with the collector-coated water-repellent auxiliary mineral particles and (2) a machine discharge product which is the component of the feed which has not been selectively oiled and is thus water-wettable.
It is taught that any mineral which may be appropriately conditioned for flotation in the presence of a reagentized feed pulp can be used as a carrier particle. Examples given include calcite, bartyes, kyanite, silica sand, anatose and fluorspar. The size of the particles used include between 14 mesh (Tyler standard about 1410 microns) and 5 microns or finer, preferably finer than 325 mesh (about 44.5 microns). The auxiliary mineral is coated with an oriented hydrophobic surface coating, of a character such that the auxiliary mineral will be floatable in the presence of the particular reagentized feed pulp which is being beneficiated. The reagent used as a collector for the minerals can be used to coat the auxiliary mineral. The examples show the use of a soap prepared from tall oil fatty acids and a suitable base as the coating agent.
It is further taught that the optimum amount of the auxiliary mineral may also vary within a wide range. The minimum amount based on the fraction of the feed to be floated is ordinarily at least an equal amount or more by weight. Further, the amount of auxiliary mineral may be equal or double or more by weight of the total feed. After flotation, the auxiliary mineral and component of the feed floated can be separated, and the auxiliary mineral can be reused for flotation after reoiling.
Duke et al., U.S. Pat. No. 3,425,546, teach a process for recycling the carrier described in U.S. Pat. No. 2,990,958. In the process, the nonoiled slimes in the froth are removed from the froth. Preferably this is accomplished by hydraulic sedimentation whereby the nonoiled slime is removed as an aqueous suspension from the oiled constituents which form a sediment. The resulting "washed" froth, which includes oiled carrier particles and an oiled constituent of the feed is filtered and dried at a temperature and for a time sufficient to place the froth residuum in a solid, pulverulent condition but insufficient to decompose or destroy either the oiling reagents or the carrier mineral. The dried froth is pulverized to a finely divided state, producing a product suitable for recycling. A portion of the recycle product is employed in combination with fresh makeup carrier and oiling reagents (for collector-coating the makeup carrier and recycle product) to condition a new charge of finely divided ore pulp for carrier froth flotation. It is taught that unless the froth is dried to pulverulent, substantially bone-dry condition, the recycled product produces poor flotation results.
Clark et al., U.S. Pat. No. 3,868,318, teach that fine particles of a mineral are separated from a mixture of fine particles, by contacting the fine mineral particles with solid bodies (carrier particles) having a mean diameter of at least 10 microns so that the fine particles of the particular mineral are preferentially adsorbed on the surface of the solid bodies, and separating the solid bodies holding the adsorbed fine particles of the mineral from the remainder of the particles. The solid bodies are preferably coarse particles of a granular form or short fibers having a length of from 1 to 2 millimeters. The solid bodies can be treated with surface-active reagents such as a long-chain amine, preferably having at least 8 carbon atoms, or a long-chain polymeric flocculant (number average molecular weight of at least 100,000), for example a polyacrylamide or a polyacrylate salt. The above separation can be done in a froth flotation process.
Unfortunately, none of the above-described references teach a process wherein valuable finely sized mineral matter can be beneficiated by froth flotation in an efficient and economical matter. There is a need for a carrier particle to aid in the beneficiation of finely sized mineral ores by froth flotation which can be recycled without further treatment. There is further needed such a carrier particle which can be used in relatively small amounts, and which can reduce the amount of the frother or collector needed for froth flotation. A carrier particle of a size which can easily be separated from the finely divided mineral ore which has been beneficiated and which does not contribute to the problem of an excessive and stable froth, is desirable.